1. Field of the Invention
The present invention relates to the generation of electrical power from submerged generators using water currents to turn the rotors of the generators, and in particular, the use of a microprocessor to set and maintain rotor pitch.
2. Description of the Prior Art
The United States, with coast lines on both sides and a network of inland rivers and lakes, has significant amounts of ocean wave and tidal power energy resources. These resources are renewable and emission free for energy production. With proper system design and deployment, ocean wave and tidal power could become one of the most environmentally friendly methods for generating electricity yet developed. The Electrical Power Research Institute (EPRI) has projected that as much as 10% of the national energy demand (400 trillion watts per year) could be harnessed from US wave and tidal current energy resources.
Waves are created by winds blowing over large bodies of water; tidal changes in the sea are generated by solar and lunar gravitational forces. As the earth rotates, the elliptical envelope shape of the ocean floor causes the water level to rise and fall. Ocean waves and tides contain tremendous amounts of kinetic energy which could be harnessed to turn generators for the production of electricity. Water is several hundred times denser than air, therefore, has more kinetic energy per unit speed. This enormous power, if harnessed to generate electricity, is fuel cost-free, non-polluting, and self-sustaining. Furthermore, tidal currents are predictable for the indefinite future; wave patterns are predictable for days in advance. Predictability is an important characteristic for an energy source used in electrical generation which is inputted into an electric grid where the supply equals demand.
The present disclosure is concerned with harnessing the kinetic energy in tidal currents which are generated by lunar and solar gravitational forces as the Earth rotates eastward. The tidal currents are to be distinguished from the powerful currents occurring in the Gulf Stream which are caused by winds, uneven temperatures, and the shape of existing land masses. Tidal currents are the periodic motion of water caused by the different lunar and solar gravitational attractive forces on different parts of the eastward rotating Earth. As these gravitational forces change, tides rise and fall causing periodic horizontal movement of water, the tidal currents. The tidal current speed varies from place to place depending on the shape of the coastline being strongest in inlets, sounds, coastal waterways, and related. Since the amount of electricity generated depends on the speed and steadiness of the water driving the generating device, the tidal currents can produce electricity only between high tides and low tides.
For the above reasons, the “capacity factor” for the tidal currents is somewhat less than, for example, powerful ocean currents as in the Gulf Stream which are constant at 4-7 MPH 24 hours per day. The EPRI has estimated that with tidal units and wind units the average power is typically between 30-40% of the “rated power” which is based on a capacity factor of 24 hours per day of continuous year long operation. While the extraction rate is somewhat low, it is well worth the effort since the energy is self sustaining, non-polluting and fuel cost-free.
Tidal kinetic energy extraction is an extremely complex operation and several devices have been proposed. Prior art most often discusses the design of these devices in terms of their physical arrangement. Water and wind turbines are generally grouped into two types: vertical-axis devices in which the axis of rotation is vertical to the ground and perpendicular to the energy stream, and horizontal-axis devices in which the axis of rotation is horizontal to the ground and parallel to the energy stream.
Generators are well known in the prior art, and similar in design and function when used in hydro-electric, wind, or ocean currents. Several models are available commercially, usable in either wind or water, provided the water unit has a water-proof housing. The kinetic energy of the water turns the rotor blades which are attached to a rotor shaft which extends into the generator. A series of step-up gears increase the rotational speed such that electricity is generated.
The rotor blades used on wind turbines tend to be long and narrow, the reason for this design is that the rotors are easier to tie down and secure during violent wind storms, not that they are more efficient in capturing kinetic energy. Since the wind turbines were developed first, it was natural that the long and narrow blades be tried in water turbine systems. However this design has encountered several problems including injury to fish and other marine species, and the blades are often structurally damaged by sea weeds and other submerged debris in the water.
Prior art turbines tested to date destroyed fish and other marine species to the extent that the devices have been nicknamed “chum machines”. The long, sweeping motion of the rotor blades tend to attract fish and injure them as they swim by in the sweep path of the rotor blades. In addition, these blades generate a lot of bubbles in the water. This is caused by cavitation, which is caused by difference in pressure gradients which forms vapor bubbles on the blade surfaces. While not lethal to fish, they are unsightly and may have some environmental impact. A recent prototype test demonstrated the structural problem when weeds, debris, and other submerged material caused the rotor blades to break.
Prior art publications can be divided into documents disclosing blades with elliptical shapes, and documents disclosing designs with blade pitch locking mechanism. Prior art disclosing elliptical shapes include U.S. Pat. No. 6,302,652, Roberts inventor, and US2008/01138206, Corren inventor. Prior art for pitch locking mechanisms include U.S. Pat. No. 5,997,253, Feeham inventor, and U.S. Pat. No. 5,611,665, Angel inventor, and U.S. Pat. No. 4,692,097, Biboliet inventor. The above references fail to at least teach or suggest the design of the presently disclosed and claimed invention.